全文获取类型
收费全文 | 28001篇 |
免费 | 2586篇 |
国内免费 | 43篇 |
专业分类
耳鼻咽喉 | 300篇 |
儿科学 | 1088篇 |
妇产科学 | 585篇 |
基础医学 | 3579篇 |
口腔科学 | 427篇 |
临床医学 | 3502篇 |
内科学 | 4739篇 |
皮肤病学 | 500篇 |
神经病学 | 2800篇 |
特种医学 | 769篇 |
外国民族医学 | 1篇 |
外科学 | 3976篇 |
综合类 | 626篇 |
一般理论 | 23篇 |
预防医学 | 3421篇 |
眼科学 | 430篇 |
药学 | 2071篇 |
中国医学 | 44篇 |
肿瘤学 | 1749篇 |
出版年
2023年 | 235篇 |
2022年 | 335篇 |
2021年 | 787篇 |
2020年 | 433篇 |
2019年 | 751篇 |
2018年 | 877篇 |
2017年 | 615篇 |
2016年 | 597篇 |
2015年 | 679篇 |
2014年 | 935篇 |
2013年 | 1321篇 |
2012年 | 1893篇 |
2011年 | 1949篇 |
2010年 | 1071篇 |
2009年 | 940篇 |
2008年 | 1518篇 |
2007年 | 1515篇 |
2006年 | 1458篇 |
2005年 | 1434篇 |
2004年 | 1290篇 |
2003年 | 1227篇 |
2002年 | 1175篇 |
2001年 | 647篇 |
2000年 | 574篇 |
1999年 | 487篇 |
1998年 | 236篇 |
1997年 | 195篇 |
1996年 | 231篇 |
1995年 | 174篇 |
1994年 | 172篇 |
1993年 | 147篇 |
1992年 | 354篇 |
1991年 | 348篇 |
1990年 | 364篇 |
1989年 | 324篇 |
1988年 | 264篇 |
1987年 | 282篇 |
1986年 | 218篇 |
1985年 | 246篇 |
1984年 | 205篇 |
1983年 | 157篇 |
1982年 | 136篇 |
1981年 | 106篇 |
1980年 | 117篇 |
1979年 | 169篇 |
1978年 | 142篇 |
1977年 | 107篇 |
1974年 | 128篇 |
1973年 | 110篇 |
1969年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Identification and characterization of a single-stranded DNA-binding protein from the archaeon Methanococcus jannaschii 总被引:3,自引:0,他引:3 下载免费PDF全文
Thomas J. Kelly Pamela Simancek George S. Brush 《Proceedings of the National Academy of Sciences of the United States of America》1998,95(25):14634-14639
Single-stranded DNA-binding proteins (SSBs) play essential roles in DNA replication, recombination, and repair in bacteria and eukarya. We report here the identification and characterization of the SSB of an archaeon, Methanococcus jannaschii. The M. jannaschii SSB (mjaSSB) has significant amino acid sequence similarity to the eukaryotic SSB, replication protein A (RPA), and contains four tandem repeats of the core single-stranded DNA (ssDNA) binding domain originally defined by structural studies of RPA. Homologous SSBs are encoded by the genomes of other archaeal species, including Methanobacterium thermoautotrophicum and Archaeoglobus fulgidus. The purified mjaSSB binds to ssDNA with high affinity and selectivity. The apparent association constant for binding to ssDNA is similar to that of RPA under comparable experimental conditions, and the affinity for ssDNA exceeds that for double-stranded DNA by at least two orders of magnitude. The binding site size for mjaSSB is ≈20 nucleotides. Given that RPA is related to mjaSSB at the sequence level and to Escherichia coli SSB at the structural level, we conclude that the SSBs of archaea, eukarya, and bacteria share a common core ssDNA-binding domain. This ssDNA-binding domain was presumably present in the common ancestor to all three major branches of life. 相似文献
152.
153.
Prevalent vertebral deformities: Relationship to bone mineral density and spinal osteophytosis in elderly men and women 总被引:4,自引:0,他引:4
G. Jones C. White T. Nguyen Prof. P. N. Sambrook P. J. Kelly J. A. Eisman 《Osteoporosis international》1996,6(3):233-239
The aims of this study were to ascertain vertebral deformity prevalence in elderly men and women and to describe the association between bone mineral density (BMD) at the lumbar spine and femoral neck, severity of spinal degenerative disease and vertebral deformity prevalence. We performed standardized spinal radiographs in a random sample of 300 elderly men and women participating in the Dubbo Osteoporosis Epidemiology Study, a population-based study of fracture risk factors. Radiographs were read independently by masked observers for the prevalence of vertebral deformity and severity of osteophytosis. BMD was measured by dual-energy X-ray absorptiometry. The prevalence of vertebral deformities was critically dependent on the criterion used. The less strict criteria seemed to overestimate deformities at either end of the spine region analysed. However, irrespective of the criterion used, prevalence of deformity was higher in men than in women (25% vs 20% for the 3 SD criterion, 17% vs 12% for the 4 SD criterion and 27% vs 25% for the 25% criterion). Femoral neck BMD was more strongly associated with vertebral deformities than spinal BMD for the 25% criterion (OR/SD change in BMD 1.39 (p=0.02) vs 1.20 (p=0.19)), 3 SD criterion (OR/SD change in BMD 1.45 (p=0.01) vs 1.10 (p=0.34)) and 4 SD criterion (OR/SD change in BMD 1.98 (p=0.0002) vs 1.68 (p=0.008)). BMD was also more strongly associated with biconcave deformities than either wedge or crush deformities and more so in men than in women. Severity of spinal osteophytosis was not associated with vertebral deformity. In conclusion, femoral neck BMD is at least equivalent to the lumbar spine BMD in strength of association with prevalent vertebral fractures. Spinal osteophytosis falsely elevates BMD without a concomitant decrease in fracture risk, indicating that any interpretation of spinal BMD needs to be adjusted for osteophytosis. These findings support the use of femoral neck bone densitometry in older men and women. Moreover, these data indicate that current criteria for radiological assessment of vertebral deformity are sufficiently loose to include a substantial proportion of non-fractures in the elderly, with important implications for the design of clinical trials. However, irrespective of the criterion used, vertebral deformities in men are at least as common, if not more so, than in women, suggesting that vertebral osteoporotic fractures are overlooked in men. 相似文献
154.
In two patients with Crohn's disease, strictureplasties had been marked operatively by a metal clip, so that definitive location on subsequent small bowel examination was possible. Each stricture-plasty presented radiologically as a short annular constriction with apparently shouldered edges and parallel lumen. Similar radiological features were found in five other patients with strictureplasties, suggesting that a pseudotumoral appearance is characteristic of strictureplasty. Attention is drawn to this finding to avoid confusion with malignancy. 相似文献
155.
Allen Cato III Linda E. Gustavson Jiang Qian Tawakol El-Shourbagy Edward A. Kelly 《Epilepsia》1998,39(1):43-47
Summary: Purpose: We wished to determine the effect of renal impairment on the pharmacokinetics and tolerability of the new antiepileptic drug tiagabine (TGB).
Methods: We assessed TGB pharmacokinetics and tolerability in 25 subjects with various degrees of renal function (based on creatinine clearance, n = 4–6 per group) from healthy (group I) to requiring hemodialysis (group V) in a single and multiple dose (every 12h), one-period (groups I-IV) or a single dose, two-period (group V) study (4-mg oral doses of TGB · HCl). Blood samples were collected after the first dose (both periods for group V) and after the last dose on day 5 (groups I-IV). TGB plasma concentrations and plasma protein binding were determined by high-performance liquid chromatography (HPLC) and ultrafiltration, respectively.
Results: TGB was well tolerated by all study subjects. The pharmacokinetics of TGB were similar in all subjects; no pharmacokinetic parameter (based on either total or unbound concentrations) was statistically correlated with creatinine clearance. For total TGB in plasma, single-dose mean values of the maximum plasma concentration, clearance, and half-life (t1/2) ranged from 52 to 108 ng/ml, from 7.14 to 11.02 I/h, and from 6.4 to 8.4 h, respectively.
Conclusions: TGB pharmacokinetics and tolerability were independent of renal function; therefore, dosage adjustment is unnecessary for epilepsy patients with renal impairment. 相似文献
Methods: We assessed TGB pharmacokinetics and tolerability in 25 subjects with various degrees of renal function (based on creatinine clearance, n = 4–6 per group) from healthy (group I) to requiring hemodialysis (group V) in a single and multiple dose (every 12h), one-period (groups I-IV) or a single dose, two-period (group V) study (4-mg oral doses of TGB · HCl). Blood samples were collected after the first dose (both periods for group V) and after the last dose on day 5 (groups I-IV). TGB plasma concentrations and plasma protein binding were determined by high-performance liquid chromatography (HPLC) and ultrafiltration, respectively.
Results: TGB was well tolerated by all study subjects. The pharmacokinetics of TGB were similar in all subjects; no pharmacokinetic parameter (based on either total or unbound concentrations) was statistically correlated with creatinine clearance. For total TGB in plasma, single-dose mean values of the maximum plasma concentration, clearance, and half-life (t1/2) ranged from 52 to 108 ng/ml, from 7.14 to 11.02 I/h, and from 6.4 to 8.4 h, respectively.
Conclusions: TGB pharmacokinetics and tolerability were independent of renal function; therefore, dosage adjustment is unnecessary for epilepsy patients with renal impairment. 相似文献
156.
Pauline M. Ryan John P. Kelly Philip L. Chambers Brian E. Leonard 《Basic & clinical pharmacology & toxicology》1996,79(5):238-240
Abstract: Oxotremorine is a muscarinic receptor agonist that induces a variety of physiological and behavioural effects including hypothermia in mice. These effects are antagonized dose-dependently by classical anticholinergic compounds such as atropine. Although the oxotremorine-induced hypothermic response has been demonstrated in mice, few studies of the effects of this muscarinic agonist have been made in the rat. The following studies were made in male Sprague Dawley rats: 1. an investigation of the dose-response relationship between oxotremorine and hypothermia; 2. an examination of the effect of housing on the oxotremorine-induced hypothermic response, and 3. an investigation of the acute administration of various doses of atropine sulphate on the hypothermia caused by oxotremorine. The results indicate that the dose-response relationship between oxotremorine and the antagonism of hypothermia is similar in rat as it is in mice. The results also showed that this effect did not occur in group-housed animals. 相似文献
157.
Focal reduction of villous blood flow in early indomethacin
enteropathy: a dynamic vascular study in the rat 总被引:3,自引:0,他引:3 下载免费PDF全文
Background—Oral indomethacin causes villousshortening, microvascular damage, and distortion, which might inducemucosal ischaemia and necrosis.
Aims—In order to determine the early events inindomethacin induced jejunal injury we examined the temporal relationsbetween morphological damage and changes in villous blood flowfollowing indomethacin.
Methods—In anaesthetised rats, mid jejunal villiwere exteriorised in a chamber and observed by fluorescence microscopy.Blood flow in surface capillaries was calculated from velocities and diameters. Indomethacin was applied by both luminal and intravenous routes for 90 minutes, after which the animal was perfusion fixed andthe villi were processed for histological examination. Control animalsreceived intravenous or luminal bicarbonate (1.25%).
Results—Blood flow slowed in individual villi at20 minutes, and progressed to complete stasis (in another group) by 45 minutes. Histological examination at 20 minutes revealed microvascular distortion, but no villous shortening: crypt depth:villous height ratios were 0.356 (0.02) in test and 0.386 (0.01) in surrounding villi(p>0.5). At stasis, the villi under study showed epithelial clumpingand were shortened: crypt depth:villous height ratios were 0.92 (0.2)in test and 0.42 (0.06) in surrounding villi (p<0.02). Vehicle alonehad no effect on either blood flow or histology.
Conclusions—Focal slowing of villous blood flowand microvascular distortion precede villus shortening and epithelialdisruption, and indicate that damage to surface microvasculature is anearly event in indomethacin induced mucosal injury in this model.
Aims—In order to determine the early events inindomethacin induced jejunal injury we examined the temporal relationsbetween morphological damage and changes in villous blood flowfollowing indomethacin.
Methods—In anaesthetised rats, mid jejunal villiwere exteriorised in a chamber and observed by fluorescence microscopy.Blood flow in surface capillaries was calculated from velocities and diameters. Indomethacin was applied by both luminal and intravenous routes for 90 minutes, after which the animal was perfusion fixed andthe villi were processed for histological examination. Control animalsreceived intravenous or luminal bicarbonate (1.25%).
Results—Blood flow slowed in individual villi at20 minutes, and progressed to complete stasis (in another group) by 45 minutes. Histological examination at 20 minutes revealed microvascular distortion, but no villous shortening: crypt depth:villous height ratios were 0.356 (0.02) in test and 0.386 (0.01) in surrounding villi(p>0.5). At stasis, the villi under study showed epithelial clumpingand were shortened: crypt depth:villous height ratios were 0.92 (0.2)in test and 0.42 (0.06) in surrounding villi (p<0.02). Vehicle alonehad no effect on either blood flow or histology.
Conclusions—Focal slowing of villous blood flowand microvascular distortion precede villus shortening and epithelialdisruption, and indicate that damage to surface microvasculature is anearly event in indomethacin induced mucosal injury in this model.
Keywords:indomethacin; jejunum; villi; microcirculation; endothelium; microthrombi
相似文献158.
159.
J D Klausner J A Sweeney M D Deck G L Haas A B Kelly 《The Journal of nervous and mental disease》1992,180(7):407-412
Numerous studies have shown evidence of cerebral ventricular enlargement in schizophrenia and its relationship to severity of clinical symptoms and psychosocial dysfunction. In this large prospective study, 88 noninstitutionalized DSM-III-R schizophrenic patients were administered a CT scan and rated for positive and negative symptomatology and premorbid adjustment. The CT scans from 14 healthy controls were used for comparison of cerebral ventricular measures. Patients had an enlarged ventricle to brain ratio of the anterior portion of the lateral ventricles, the frontal horns, compared with controls. Patients with larger frontal horns had more severe negative symptoms and poorer premorbid childhood adjustment. The area of the main body of the cerebral lateral ventricles, though not elevated in patients, was correlated with the total number of prior hospitalizations. These results support the hypothesis of a structural and functional "frontal" deficit in schizophrenia. 相似文献
160.
Cerebellar syndrome in myxoedema revisited: a published case with carcinomatosis and multiple system atrophy at necropsy. 下载免费PDF全文
N Quinn R O Barnard R E Kelly 《Journal of neurology, neurosurgery, and psychiatry》1992,55(7):616-618
One of six patients in a 1960 paper on "Cerebellar syndrome in myxoedema" was subsequently found to have adenocarcinoma. General post-mortem revealed carcinomatosis and basal pneumonia. Neuropathological examination revealed the changes of multiple system atrophy. The relationship between hypothyroidism, carcinoma, and cerebellar, pontine and striatonigral degeneration is discussed. 相似文献